Doublexbase p propellants



Jan. 11, 1966 H Y ETAL 3,228,815

F INCREASED BURNING RATE DOUBLE-BASE PROPELLANTS O CONTAINING BENZOPHENONES 5 Sheets-Sheet 1 Filed Oct. 21, 1957 5a wmzwwmmm O O O O O O O O O O m w m a 6 nN O nun O \H MAE! Om O BURNING RATE, lN/SEC Jan. 11, 1966 DOUBLE-BASE PROPELLANTS OF INCREASED BURNING RATE Filed 001;. 21, 1957 R. A. HENRY ET AL 3,228,815

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EXAMPLE c o o r- BURNING o "I o lN SEC RAT INVENTORS RONALD A. HENRY WILLIAM S. MC EWAN ATTORNEYS Jan. 11, 1966 HENRY ET AL 3,228,815

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BURNING RATE, lN/SEC United States Patent 6 T 3,228,815 BASE PROPELLANTS F INCREASED BURNING RATE CONTAINING BENZOPHENONES Ronald A. Henry and William S. McEwan, China Lake, Calili, assignors to the United States of America as represented by the Secretary of the Navy Filed Oct. 21, 1957, Ser. No. 691,521 4 Claims. (Cl. 149-98) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a method for increasing the burning rate of nitrocellulose-base propellants, and to new nitrocellulose-base propellent formulations having improved burning rates.

A great deal of research is being directed toward increasing the burning rate of solid propellants for rockets 'in the zone of useful rocket pressures, roughly, between 7003,000 p.s.i. Faster burning rates are important in the interest of increased thrust and thereby increased range of the rocket without added weight of propellant.

Various additives have been used in the past to increase the burning rate of solid propellants. The difiiculty in finding suitable additives for this purpose is due to the fact that the additive must not prohibitively affect such critical properties of the propellant as stability, calorific value, and ballistic characteristics. The relatively recently developed plateau and mesa type propellants are examples of propellants possessing ballistic properties which are highly sensitive to the addition of even small amounts of additives. These latter propellants are characterized by an unusual pressure-burning rate relationship, this relationship defining the plateau and mesa characteristics. The pressure burning rate relationship is defined by the slope n, or pressure exponent, of the curve produced by a logarithmic graph of the burning rate of propellant plotted against pressure. The relationship is particularly important in the zone of useful rocket pressures. The relationship between the pressure at which a propellant burns and its burning rate is mathematically expressed as r cp or as Log r=n Log p+log c, where r is the burning rate, p is the pressure at which the burning rate is measured and c and n are constants characteristic of a given propellant. A plot of Log r against Log p for conventional type propellants, for example, produces a straight line of slope n, that is, there is a progressive increase in burning rate for each increase in pressure. However, in the case of plateau type propellants the pressure exponent becomes zero in a certain useful region of pressure. In the case of the mesa type propellant the pressure exponent becomes zero at some point and then reaches a negative value thereafter in the region of useful rocket pressures so that the burning rate in this negative slope region actually decreases with increase in pressure. The plateau and mesa phenomena are due to the presence of critical amounts of certain lead compound modifiers, the phenomena being extremely sensitive to the addition of foreign substances to the propellant composition. There are a number of now well known advantages to propellants exhibiting the above phenomena.

The burning rate of some solid propellants can be increased by increasing their calorific value (heat of explosion). However, with mesa or plateau-type propellants the beneficial effects of the ballistic modifiers which produce the mesas and plateaus are gradually lost or dissipated as the heat of explosion increases; in other words there are limits beyond which the usual metal salt modifiers cannot be satisfactorily employed. The

3,228,815 Patented Jan. 11, 1966 burning rate of double-base propellants can also be increased by adding burning rate accelerators such as guanidinium S-nitroaminotetrazole, nitroarninoguanidine, S-aminotetrazole, potassium dinitroacetonitrile, certain coordination compounds of cobalt, etc. These accelerators are normally used at concentrations ranging from 5 to 50 percent. Because these compounds are insoluble in the propellant matrix and cause an opaqueness, they vitiate the mesa or plateau in those double-base formulations which normally show this phenomenon. Some of these accelerators also cause propellant instability. Burning rates can be increased in some cases by adding certain finely divided metals, such as aluminum, magnesium, boron, etc., but such materials again tend to eliminate the desirable mesa effects if used in quantities needed to get really significant boosts in burning rate. Fine metal wires can also be dispersed throughout a double-base propellant to elfect substantial increases in the normal burning rate without, in this case, vitiating the mesa; however, the rate is not increased in the mesa region.

It is an object of this invention to provide a method for increasing the burning rate of solid propellants without prohibitively altering other required characteristics of the propellants.

It is another object of this invention to provide improved propellent compositions containing additives which increase their burning rates and do not prohibitively affect other required properties of the propellants.

The above objects have been accomplished by incorporating into conventional solid propellent formulations up to about five percent of certain propellant-soluble ultraviolet light absorbers.

The invention is best understood by reference to the following description taken together with the accompanying drawings in which:

FIGS. 1-5, inclusive, present graphs of pressure-burning rate curves for the N5 propellent formulation used to illustrate this invention and for this formulation modified in various ways, including the addition thereto of ultraviolet light absorbers, to illustrate the effectiveness of ultraviolet light absorbers in producing superrate burning. The curves bear example numbers to indicate the examples in the tables to which they correspond.

During an investigation to ascertain the mechanism by which certain lead salts produced super-rate burning in mesa or plateau-type double-base propellants, it was discovered that light or radiant energy played an important role in the reactions leading to super-rate burning. Furthermore, this photochemical reaction was found to occur in the depths of the solid propellant, below the decomposing and burning surface. This discovery lead to the prediction that the addition of small amounts of propellant-soluble, organic compounds which strongly absorb ultraviolet light would markedly influence the reactions leading to super-rate burning.

The ultraviolet light absorbers used to illustrate the invention are hydroxy and alkoxy substituted benzophenones. The percentage composition limits of the double-base propellant, N5, used to illustrate the invention are as follows- Component: Wt. percent Nitrocellulose 4460 Nitroglycerin 28-47 Non-explosive plasticizer 315 Stabilizer 1-5 Ballistic modifier 2-5 The non-explosive plasticizer may be diethyl phthalate, dibutyl phthalate, dimethyl sebacate or others. The stabilizer is 2-nitrodiphenylamine. The ballistic modifier may be lead salicylate, lead Z-ethylhexoate, lead acetyl- 3 salicylate, lead 2,4-dihydroxybenzoate and certain other lead salts. The actual composition of N-S used in the examples is the following g z g' (126 N percent) 5 ultraviolet light absorber A. Comparison of the curves Nitroglycerin 34.8 of Ex mples IX and with the curves for other exam les Diethyl phthalate 108 hows that the ultraviolet light absorbers produce their zmitrodiphenylamine 20 best effect in the absence of other stab1lizers such as 2- Lead salicylate L2 t o lp enylamlne. These two examples also illustrate Lead 2 ethy1hexoate L2 he r uced elfect resulting from an excess of ultraviolet Candelma Wax 2 light absorbers, 2-mtrod1phenylam1ne itself being an ultraviolet light absorber. The N-5 propellant is presently being used in large FIG. 4 presents the pressure-burning rate curves for quantities by the Armed Forces in the 2.75-inch folding x pl XPXIV, inclusive- T e Curv s for N-S and fin aircraft rocket known as the Mighty Mouse," and Example III'are also presented for comparative purposes. which is disclosed in US. Patent No. 2,801,587. Examples XI and XII are N-S compositions modified The examples given in the following table are illustraby the substitution for lead salicylate of Pb S-(Z-carboxytive of the invention but not limiting thereof. The forphenylazo) salicylate and Pb 5-(phenylazo)salicylate, remulations were made by simply incorporating the ultraspectively, in amounts such that the total lead content violet light absorber in the propellent mix which was of the N5 composition is unchanged. Examples XIII made .by a solvent process. and XIV are the compositions of Examples XI and XII, Table 4. curves for Examples I and III and for N-5 are included for comparative purposes, Example I being N-S formulation without 2-nitrodiphenylamine and Example III being the example containing the optimum amount of Ingredient Examples (wt. in grams) VII VIII XIII XV Nitrocellulose Nitroglycerin Diethyl phthalate Lead salicylate. Lead 2-ethylhexoate Lead 5-(2-carboxyphenylazo) salicy Lead 5-(pheny1azo) salicylate- 2-nitrodiphenylamine Candelilla wax U.V.L. absorber A* 2,tdihydroxybenzophenone 2,2,4,4-tetrahydroxybenzophenone 2,2-dihydroxy-4,4-dimethoxybenzophenone *Mixture of 2,2-dihydroxy-4,4-dimethoxybenzophenone and 2,24,4-tetral1ydr0xybenzophenone. Reference is made to FIG. 1 which presents the pres- 40 respectively, modified by substituting ultraviolet light absure-burning rate curves for N5 and for compositions of Examples I-V, inclusive. Example I, which was included for comparative purposes, does not contain any 2-nitrodiphenylamine. It will be noted that the curve presents the characteristic mesa phenomenon but the burning rate is lower than that of N-S. Examples II-V, inclusive, contain no Z-nitrodiphenylamine but do contain varying amounts up to five percent by weight of the ultraviolet light absorber A which is a mixture of 2,2-dihydroxy-4,4- dimethoxybenzophenone and 2,2,4,4'-tetrahydroxybenzophenone. It will be noted by comparison of these curves with those for N5 that the presence of the ultraviolet light absorber markedly increases the burning rate in the mesa region in all cases, with the exception of Example V, with some shift in the mesa, and that Example III, containing two weight percent of additive, gives the rnost pronounced eliect. Increasing the amount of ultraviolet light absorber to five percent destroys the beneficial mesa ballistics.

FIG. 2 gives comparative showings of the pressureburning rate curve for N-S and curves of N-S formulation modified by the addition thereto of other ultraviolet light absorbers. The curve for Example III, the formulation containing the optimum amount of ultraviolet light absorber A is included for comparative purposes. The ultraviolet light absorbers used in Examples VI, VII and VIII of FIG. 2 were 2,4-dihydroxybenzophenone, 2,2,4,4:- tetrahydroxybenzophenone and 2,2'-dihydroxy-4,4'-d1- methoxybenzophenone, respectively. It will be noted that in all cases a significant increase in burning rate in the mesa region was achieved over the burning rate of unmodified N-S.

FIG. 3 presents the pressure-burning rate curves for Examples IX and X containing two grams each of both 2-nitrodiphenylamine and an ultraviolet absorber. The

sorber A in equal amount for 2-nitrodiphenylamine. It will be noted that a Well defined increase in burning rate is obtained by addition of the ultraviolet light absorber A. The four examples show that ultraviolet light absorber A is effective when used in combination with lead salts other than lead salicylate.

FIG. 5 presents curves for N5 propellant, N5 propellant with the Z-nitrodiphenylamine removed (Example I), and for N5 composition with both 2-nitrodiphenylamine and the lead salts removed (Example XV). EX- ample XV contained about two weight percent of ultraviolet light absorber A. The graph illustrates that when both the stabilizer (2-nitrodiphenylamine) and the ballistic modifiers (lead salicylate and lead Z-ethylhexoate) are omitted from the basic N-5 formulation, super-rate burning is completely lost. When only the 2-nitrodi- .phenylamine is removed the super-rate burning is both decreased and shifted to lower pressures. The graph clearly indicates that the ultraviolet light absorbers are not by themselves ballistic modifiers; they only influence, perhaps synergistically, the behavior of the lead salts.

Taliani stability tests indicated that all of the formulations containing rate booster additions are sufficiently stable for use as propellants.

While the invention has been illustrated by the use of specific ultraviolet light absorbers, the hydroxy and alkoxy substituted benzophenones, it is not limited to the use of these compounds, as other ultraviolet light absorbers may be used.

The invention is not limited in application to propellants containing nitroglycerin as certain other polynitrate esters may be employed as the high energy plasticizer. Neither is it limited to the particular double-base propellant, N-S, used to illustrate it, as it is effective with other double-base mesa or plateau type propellants.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. Propellant formulations comprising from about 44- 60 percent nitrocellulose; from about 2847 percent nitroglycerin; from about 2-5 percent of ballistic modifier selected from the class consisting of lead salicylate, lead 2-ethy1hexoate, lead aoetylsalicylate, lead 2,4-dihydroxybenzoate, and mixtures thereof; and from about 1-5 percent of a benzophenone having the formula OH R wherein R represents a member from the group consisting of lower alkoxy and hydroxyl, R is a member from the group consisting of hydrogen, hydroxyl, and lower References Cited by the Examiner UNITED STATES PATENTS 2,440,327 4/ 1948 Crawford. 2,574,479 11/1951 Hickman. 2,628,561 2/1953 Sage et al 520.5 X

FOREIGN PATENTS 485,662 8/1952 Canada.

LEON D. ROSDOL, Primary Examiner.

20 B. R. PADGETT. Assistant Examiner. 

1. PROPELLANT FORMULATIONS COMPRISING FROM ABOUT 4460 PERCENT NITROCELLULOSE; FROM ABOUT 28-47 PERCENT NITROGLYCERIN; FROM ABOUT 2-5 PERCENT OF BALLISTIC MODIFIER SELECTED FROM THE CLASS CONSISTING OF LEAD SALICYLATE, LEAD 2-ETHYLHEXOATE, LEAD ACETYLSALICYLATE, LEAD 2,4-DIHYDROXYBENZOATE, AND MIXTURES THEREOF; AND FROM ABOUT 1-5 PERCENT OF A BENZOPHENONE HAVING THE FORMULA 